The present invention relates generally to magnetic recording media and, in particular, to apparatus and techniques for testing the glide height characteristics of magnetic recording media.
Disc drives are the primary devices used for mass storage of computer programs and data. Within a disc drive, a load beam supports a hydrodynamic air bearing slider close to a rotating magnetic disc. The load beam supplies a downward force that counteracts the hydrodynamic lifting force developed by the slider's air bearing. A gliding action is brought about as a layer of air, dragged along by the spinning disc surface, is compressed between the surface of the disc and the adjacent surface of the magnetic head. As a result of the gliding action, the magnetic head rides at a distance from an adjacent magnetic disc surface. That distance must be small enough to allow high density recording while preventing damage that would otherwise be caused by contact between the spinning disc and the magnetic head.
High a real densities currently are achieved by lowering the separation between the disc and the head to less than twenty nanometers (nm). However, some level of disc roughness is required to reduce adhesive forces when the head is at rest. The level of disc surface topography must, therefore, be kept within a tight range to fly the head safely at low altitudes while simultaneously preventing it from sticking to the disc surface when the head is at rest. The topography of the disc surface is, therefore, critical to the proper operation of the disc drive.
As part of the process of manufacturing hard files, the quality of a magnetic disc 10 is provided by determining the glide conditions which can be established between the disc and a glide head 12 (FIG. 1). In particular, the effect of outwardly projecting defects on the surface of the magnetic disc is studied during glide height testing. When such defects are large enough to close the gap between the magnetic disc and the glide head, the defects strike the glide head. The movement of the glide head can be sensed, for example, by a piezoelectric transducer, which generates an electrical signal indicating the adjacent passage of an outwardly projecting defect.
The distance "h" measured from lower surface 14 of the glide head 12 to the upper surface of the rotating rigid disc 10 is known as the "fly" height. The "fly" height of a glide head is critical to the accurate performance of glide tests and depends, among other things, on the "Z" height. The "Z" height" is the distance from the bottom of the mounting base 16 for the glide head 12 to the upper surface of the glide disc 10. The glide head 12 is coupled to the mounting base 16 by a load arm 18. As illustrated by FIG. 2, variations in the "Z" height can cause significant, and unacceptably large, changes in the "fly" height. Such variations in the "Z" height can occur, for example, as a result of movement of the mounting base 16 and make it difficult to ensure the accuracy and uniformity of "Z" height settings for different glide testers. Moreover, variations in the "fly" height for glide heads can result in the false reporting of defects or in the failure to detect defects on the disc surface.
Accordingly, improvements in glide heads are desirable to provide better accuracy in the detection of defects on the surface of discs.